1. Field of the Invention
The present invention relates to an electric power supply cut-off circuit for cutting off the electric power supply from the outside when any abnormal situation arises in IC, and a liquid droplet discharge apparatus which includes such an electric power supply cut-off circuit.
2. Description of the Related Art
A variety of electronic elements are arranged at a high density in IC such as driver IC for driving an electronic apparatus such as a liquid droplet discharge apparatus. Therefore, any unintended transistor (parasitic transistor) is formed between a plurality of elements in the driver IC in some cases. When such a parasitic transistor is formed, any excess current flows through the driving device (latch up) due to the amplifying function of the parasitic transistor. It is feared that the driver IC may excessively generate the heat, and the driver IC may ignite in the worst case.
In order to avoid the excessive heat generation and the ignition of the driver IC as described above, a certain apparatus includes, in the driver IC, a circuit (thermal shutdown circuit) which is provided to stop the driver IC when the temperature of the driver IC is higher than a predetermined temperature. For example, in the case of a power source IC described in Japanese Patent Application Laid-open No. 2005-38921, an Nch-MOS transistor is connected to a thermal shutdown circuit composed of an NPN bipolar transistor. The leak current of the Nch-MOS transistor is increased as the temperature of the power source IC is raised. When the leak current of the Nch-MOS transistor is not less than 1 μA, then the thermal shutdown circuit is operated, and the operation of the power source IC is stopped.
However, in Japanese Patent Application Laid-open No. 2005-38921, the NPN bipolar transistor, which is incorporated in IC, is used as the thermal shutdown circuit. Therefore, if any parasitic transistor as described above is formed between the NPN bipolar transistor and any other element in IC, it is feared that the NPN bipolar transistor may not be operated normally, and it is impossible to stop the operation of IC.